"This momentary indiscretion has jeopardised the most important thing in my life, the person I love and respect the most, Rob," she said. "I love him, I love him, I'm so sorry."

It has now been claimed that Stewart confessed all to her Twilight co-star late last week before the story broke, leading to a tense confrontation backstage at Sunday's (July 22) Teen Choice Awards in LA.

"Rob and Kristen were having a long and intense conversation backstage, and he looked miserable, heartbroken and humiliated," a source told The New York Post. "She was pleading."